The present invention relates to a shock absorber such as a hydraulic shock absorber that generates a damping force by controlling the flow of a fluid against the stroke of a piston rod.
In general, shock absorbers attached to the suspension systems of automobiles or other vehicles are arranged as follows. A piston connected with a piston rod is slidably fitted in a cylinder having a fluid sealed therein, and the flow of fluid induced by sliding movement of the piston in the cylinder is controlled by a damping force control mechanism, which comprises an orifice and a disk valve, to generate a damping force against the stroke of the piston rod.
In a hydraulic shock absorber disclosed in Japanese Patent Application Publication No. 2006-10069, for example, hack-pressure chamber (pilot chamber) is formed at the hack of a main disk valve serving as a damping force generating mechanism. A part of the flow of fluid is introduced into the back-pressure chamber to apply the pressure in the back-pressure chamber to the main disk valve in the direction for closing the valve, and the pressure in the back-pressure chamber is controlled by a pilot valve, thereby controlling the valve opening of the main disk valve. Thus, it is possible to increase the degree of freedom for adjusting damping force characteristics.
The shock absorber, in which the valve opening of the main valve is controlled by the pressure in the back-pressure chamber, as disclosed in Japanese Patent Application Publication No. 2006-10069, suffers, however, from the following less useful aspect. In the above-described shock absorber, when the main valve opens, the volumetric capacity of the back-pressure chamber reduces for structural reasons. Therefore, when the main valve opens, the pressure in the back-pressure chamber is likely to increase excessively, making it impossible to obtain desired damping force characteristics.